Human blood is made up of approximately 35 percent cellular components, including red cells, white cells, and platelets with the remaining 65 percent being a fluid called plasma. The plasma suspends the cells and platelets and comprises a solution of approximately 90 percent water, 7 percent protein, and 3 percent various other organic and inorganic solutes.
The protein portion of plasma consists of various different protein fractions including, for example, albumin, fibrinogen, gamma (.gamma.) globulin, alpha (.alpha.) and beta (.beta.) globulins, and others.
For various human therapies, it can be desired to separate and concentrate blood protein fractions so that only a selected single fraction is administered to a patient. For example, it can be particularly desirable to separate albumin from the plasma and provide the separated albumin in a concentrated solution for patient therapy.
Methods for separating protein fractions from plasma are disclosed in U.S. Pat. No. 2,390,074 to E. J. Cohn and in E. J. Cohn, L. E. Strong, W. L. Hughes, D. J. Mulford, J. N. Ashworth, M. Melin and H. L. Taylor, Separation Into Fractions of Protein and Lipoprotein Components, J. Am. Chem. Soc. 68 (1946), p 459-475. Both U.S. Pat. No. 2,390,074 and the American Chemical Society article are incorporated herein by this reference. The protein fractions are separately precipitated by adding a precipitating agent or precipitant such as ethanol to the plasma and maintaining the plasma solution at a desired pH, temperature, ethanol concentration, and ionic strength to precipitate the desired fraction.
The Cohn process is essentially a batch process where the various proteins are precipitated from the solution sequentially. The proteins are grouped into fractions with as much as possible of the fibrinogen in the plasma precipitated first as Fraction I. Next, Fractions II and III which are designated the .gamma. globulin fractions are precipitated together. Fraction IV-1, rich in lipid and .alpha.-globulins, is then precipitated, followed by precipitation of remaining .alpha.-globulins in combination with .beta.-globulins as Fraction IV-4. Albumin remaining in the supernatant (centrifugate) is next precipitated as Fraction V to obtain a concentrated albumin fraction.
In each case, after the desired fraction is precipitated, the conditions of the supernatant plasma are changed to precipitate the next fraction.
During the time interval required to adjust the supernatant to its equilibrium condition for the next precipitation, protein fractions that desirably remain in solution can precipitate. For example, when the supernatant is being adjusted to conditions for precipitating an earlier fraction, albumin can precipitate, thus contaminating the earlier fraction and also reducing the amount of albumin that can finally be recovered. Additionally, batch processes can be slower than desired.
Thus, there is a need in the art for a simple and efficient process for precipitating protein fractions continuously that maximizes the amount of protein of a desired purity recovered.